1. Field of the Invention
The present invention relates to a rubber composition, a rubber roller comprising the rubber composition and a method of manufacturing the rubber composition. More particularly, the present invention relates to a modification of the rubber composition for use in paper-feeding rubber rollers of office appliances such as laser printers, electrostatic copying machines, facsimiles using ordinary paper and automatic deposit payment machines (ATM).
2. Description of the Related Art
The rubber composition for use in the paper-feeding rollers of office appliances such as laser printers, electrostatic copying machines, facsimiles and automatic deposit payment machines (ATM) is demanded to have high wear resistance and friction coefficient. In recent years, especially office appliances for personal use are in wide use and various kinds of paper are used therefor. Thus, the rubber roller is demanded to have high wear resistance and friction coefficient to feed various kinds of papers reliably. When the surface of the paper-feeding rubber roller is worn owing to repeated use, the friction coefficient thereof deteriorates, and hence slip occurs, which deteriorates the paper-feeding force greatly. Further, it is necessary that the rubber roller does not deteriorate in its performance applying a load at a high temperature. That is, the rubber roller is required to have a low permanent compression set.
Thus, in order to provide the rubber roller with a high friction coefficient and a high wear resistance, there have been proposed rubber rollers comprising a rubber composition formed of a sulfur-vulcanized mixture of a rubber material and thermoplastic elastomer. For example, it is known that EPDM rubber is used as the rubber material and urethane thermoplastic elastomer (TPU) is used as the thermoplastic elastomer. Further it is known that styrene butadiene rubber (SBR) is used as the rubber material and urethan thermoplastic elastomer (TPU) is used as the thermoplastic elastomer.
However, because the TPU is hard, the hardness of each of the rubber rollers composed of these rubber compositions cannot be lowered to an appropriate degree and hence the it is impossible to provide the rubber rollers with a preferable paper-feeding performance. In the rubber rollers, the rubber composition vulcanized with sulfur has blooming to a high extent, which causes the friction coefficient of the rubber roller to deteriorate.
Further, because matrix resin consists of urethane, it is necessary to reduce the amount of the matrix resin to allow the rubber roller to have a low hardness required for roller use. Thus, a problem occurs in kneadability. Further, there is another problem that because the friction coefficient of urethane is not so high, the rubber roller is prevented from having an appropriate friction coefficient.
Further, it is known that a rubber composition comprises thermoplastic crystalline poly-olefin and EPDM rubber vulcanized with phenol resin vulcanizing agent. However, when a rubber roller comprising the rubber composition is used as a paper-feeding roller, generation of blooming can be restrained. But the poly-olefin serving as forming matrix, namely, polyethylene and polypropylene are hard. Thus, it is impossible to reduce the hardness of the rubber roller sufficiently and hence the rubber roller is incapable of having a preferable paper-feeding performance.
As described above, efforts have been made to enhance the friction coefficient of the rubber composition or the rubber roller and reduce a permanent compression set by blending vulcanized rubber such as vulcanized EPDM rubber and thermoplastic resin or thermoplastic elastomer with each other. But a paper-feeding rubber roller which is so soft as to obtain a high friction coefficient for contact of paper and does not give rise to blooming and is superior in wear resistance has not been developed. It is described in the above patent publication that the permanent compression set can be improved. But as a result of examination, it was revealed that the paper-feeding performance of the rubber roller was not reliable when it was left with applying a load thereto at a high temperature, supposing that the rubber rollers are transported to a client.